Sound absorbing wall treatment



April 12, 1938. c. L. NEWPORT ET AL 2,113,924

SOUND ABSORBING WALL TREATMENT Filed Dec. 6, 1957 2 Sheets-Sheer, 1

INVENTORS.

April 12,1938.

c. 1 NEWPORT ET AL SOUND ABSORBING WALL TREATMENT 2 Sheets-Sheet 2 Filed Dec. 6, 1957 INVENTORS M 25 W Patented Apr. 12, 1938 I PATENT OFFICE SOUND ABSORBING WALL TREATMENT Charles L. Newport and Herbert G. Smith, Los

- Angeles, Calif.

Application December 6, 1937, Serial No. 178,310

' Claims.

Our invention relates to sound absorbing treatments for walls and more. particularly for those 'walls, such as the back walls of theatres, where high efficiency is required over a wide range of 5 frequencies.

An object of the invention is to provide an acoustical treatment adapted for absorbing both high frequency and low frequency sounds, and for this reason to provide for employing appreciable thicknesses of rock-wool, or the like, properly protected by a durable and decorative covering which is fire-proof but non-metallic For high absorptivity over a wide range it has been the custom to cover rock-wool or felt with screening, perforated metal, fabric. and the like; I

construction to pre-fabricated articles of manufacture.

It is an object of this invention to provide for covering rock-wool or the like with a readily applied and readily perforated covering which in addition to passing sound to be absorbed by the underlying layer is given to absorption through diaphragm action as well as to absorption by reason of its cellular and foraminous characteristics and which tends to transmit, rather than to reflect.

. Rock wool is known to have high predetermin'able efliciency for absorption of given frequencies whcnits density is known and his a particular object of this invention toprovide for retaining rock wool within a wall under a compression which is predetermined during construction.

construction for carrying out the foregoing objects and which is readily applied to existing v suitably displaced during the application of the walls.

In carrying out our inventionwo provide, in

contact with the wall, co-extensive pads of rock wool, vfelt or the like, held under predetermined compression and held against settling by coarse -wire mesh or the like stretched over the outer surface thereof. By building the wool up to a I fiopredet'ermined thickness before the mesh is stretched over it, and by-properly,-furring the mesh with respect to the wall, we areable'to closely predetermine the density and the sound absorbing characteristics of the wool; Naturally 5 too low a-density gives ample porosity but insuf- Another object of the invention is toprovide .a'

ficient total fibre-surface, Too high a density gives ample fibre surface but insufficient porosity or penetrability. Therefore by applying wool of known physical characteristics to a given depth on the wall, and then compressing it a known degree when applying the mesh, the final result is predetermined. v

The wire mesh may be relatively light weight, inexpensive, and non-decorative since it' is'to be totally obscured, but we cause the mesh to serve a dual function by employing it as an anchor and reenforcement for the final covering. When the mesh has been applied the rock wool or like material actually contacts the mesh and even projects slightly through the large openings provided in the coarse mesh. r

The next step in our method consists in applying over the mesh an acoustical plaster, as dis tinguished from non-absorptive coverings, and preferably this plaster is of such nature that when fully dried it'will prove suitably flexible. .Another requirement is that the plaster, as it is applied by usual means, will be capable of displacing the wool slightly so that the plaster will flow behind the wire mesh and will become anchored or keyed theretoso that thefinal covering is a layer of 'wire-reenforoed plaster of suitable resistance combined with suitable flexibility and absorption. The plaster employed may be that described inthe'PateritNo. 1,960,880, issued to one of the applicants, Herbert C. Smith.

While there are numerous plasters which will suggest themselves tothe minds of those skilled in the art, we have'found that aplaster composed of a large percentage by bulk of rock wool is well suited, For instance, a mixture of granulated rock-wool and a binder such as one of the magnesium cements, makes an ideal plaster for the purposes of this invention. Such a plaster by reason of the large bulk of "water-saturated rock. wool pellets, adds enough moisture tothe originally installed rock woolto insure its being plastic -.covering. Also this plaster may betrow- 'vidlngthe required f nal porosity when ,dry; A

further object and advi'antage, of the\-rock wool plaster is that it peculiarlyadapted for subse-. quen'tsteps', L v

plaster, in being applied is preferably stippled by being pressed-throughout: its surface tdprovide a ,suit? texture .-is required-or not,: the finalistep iniour being applied, orshortly after 'ablydecorativeltextureh However, whether this V ous, suitably numerous and yet so irregularly distributed as to avoid the stereotyped appearance common to mechanically perforated wall surfaces.

Obviously, by filling shallow open-face pans, boxes, tile, or the like with rock wool; stretching wire mesh over the now filled receptacle; applying the plaster, and then finally stippling the same all according to our invention, a pre-fabricated sound-absorbing tile may be produced. We have found, however, that lower costresults where the complete'combination canbe produced I directly upon the wall. by artisans of ordinary skill.

In some instances where characteristic absorption is required, we propose \to substitute for the wool a removable core, which may be withdrawn when the plaster-has set, or after the plaster has behind the plaster. The result is a diaphragm,

been'perforated, so asto leave an.air space only of acousticplasterof suitablestrength and which provides absorption partly by reason of its diaphragm aetion, partly-by; reason of its porous "nature, and partly by -reason of the air space behind it." a

'L To illustrate: one. application'fof our invention .we haveshownxin the accompanying. drawings a wall treated. according: to our invention.

' a hardsw'all plaster surface ..backed byjcommon stulidingli. -To thesurface of this wall is applied In the drawings:

, Figurel is ahorizontalsectional view of the g I increased thickness of plaster.

wall.

tile embodying-features.of our invention. v

The numeral i indicates a common reflective wall surface to'be treated this being, for example,

1 a plurality of's'pace'd iurririg strips I; o'neffor and aline'd witheach stud 6 fand'heId directly thereto by a-longln'ail' orspikesuchas 8.sothat the comv .plete acoi'isticalftreatmentj about to described 'becomesi-afsubstantiaily integral part of the old wall,

Between; the .furring strips th e' rock-woolv 9 is. provided, this-being readily appliedin batt or roll 'fo'rmand built'jup to. -g'a'n1 originalthickness such that it exte'nds beyon the outer surfaces Ta of the furringstrip's 'as indicated in Figure- 3., -'.'I'he depth to which this ,wool'- is b l1l1t '11D.dp6l'ldS ordinarily applied,'--,a"s companedwith the final" density required.

'The wir'e mesh is indicated at I0 and may be common hex-mesh or chicken wire'. stretched; tightlyacross the furring strips and co exten 'sivelyof the entiresurface being treated." This wire is held in 'place by thejafore'sa'ld. nails 8 but I with the; aid of any' well known furring' device,- such asindicated'at H this-wireijs 'iurred away from" the Srnp JL-Dspite thi'sfurring of'the Wire from the'st'rips I, the rock-wool contact: the

' wiremesh and is aetuallyheld under'eompression tn byt-this method T -holding the-wool also serving' to prevent the, wooll fromnsettlirig, and,

plastering large wall surfaces so treated it is found that the Workman of usual skill can apply.

the plaster with suitable economy and can produce a decorative layer fully obscuring the furring strips, the wire mesh, the nails, and the wool respectively and can provide predetermined thickness to the finished plaster.

It will be noted that the resiliency of the wool at spaces intermediate of the studs results in the plaster at points intermediate of the furring strips being only of the required thickness while directly over the furring strips the plaster is of greater thickness.

Since the furring strips are not covered with wool it is decidedly advantageous that the higher reflectivity of the furring strips be offset by increased thickness of plaster, while to employ over the wool this same thickness would not only prove wasteful of plaster but would partially defeat the purpose of the underlying layer of rock- From the foregoing, and from the existing knowledge of perforated acoustical plaster, it will be apparent that that portion of' the treatment directly overlying the furring strips will show very appreciable absorption while that/portion of the treatment between the iurring strips provides novel results.

To apply a 'stippling brush or the like (not shown) to provide the through apertures, it is preferable to allow the plaster to take an initial set so. that the apertures do not close over as the penetrating instruments are withdrawn.

'While the plaster is then harder than when first applied, we find that a rock-wool composition plaster is readily penetrated while the compressed resilient backing of rock wool permits of rapid" penetration without damage to the covering as a that 'we have provided: (1) a perforated acoustical plaster .as the sound receiving side of the treatment, (2) a wire re-enforced diaphragm. of- -relatively'. slight depth and which is reenforced an'd'damped by an underlying layer of rock wool;

' (3) a suitably decorative outer. surface having the general appearanceor surface texture common to accepted acoustical'plasters, (4), aninner concealed layer of felt or'rock Wool, of controlled density but which is' in suitably direct communi cation'fwith the source of sound, (5) a highlyreflective backingbehind the wool and in the =form of a hard plaster wall which being damped,

by the wool. will not tend to transmit. appreciable sound and which will thereby act to reflect unposed respectively of transverse end walls l6, vertical ribs 11, and a wire mesh ll stretched over the outer face of the frame and properly furred. Broken lines is indicate removable cores which are in place only during manufacture and which are removed when the plaster web 20 is suitably set and finished. The resultant product has only the air space 2| behind the originally plastic, wire reenforced diaphragm, although it is obvious that rock wool or other sound absorbing filler may be added to the air space 2! ifrequired.

In practice we have found that the acoustical treatment hereindescribed shows its maximum absorption at about 512 d. v. and is therefore peculiarly suited to treatment of the back walls of sound-picture theatres. With this fact in view, care is exercised in applying the acoustical plaster and in predetermining the compression to which the rock wool is subjected, so that the plaster is built up to just the right thickness to have what we believe to be a diaphragm action in contact with the wool so that the plaster and wool cooperate to show high absorption of the strong low frequency sounds. While such a combination shows unexpected absorption at low frequeneies it would ordinarily be expected that the combination would be so inefflcient at higher frequencies as to be quite impractical in theatres where music is produced in addition to speech. However, our product does show suitable absorption at the higher frequencies and this we believe to be due to our having provided the apertures extending through the plaster which at their margins produce some absorption of high frequencies, and which apertures allow other portions of the high frequency energy to pass through to the rock wool.

Therefore the product is unique in that while the acoustical plaster in contact with the wool shows higher absorption at low frequency than would the plaster alone, thehigh frequency efficiency of the underlying wool is not reduced as much as would be expected by reason of the plaster acting to transmit appreciable percentages of high frequency energy rather than reflecting same to disadvantage.

We claim:

1. In combination with a wall having spaced projections thereon and a covering of relatively highly compressible sound absorbing material between said projections, a meshed fabric covering said sound absorbing material and spaced from the wall by said projections, and a layer of sound absorbing plaster covering and keyed to said fabric, said layer of plaster being sufficiently flexible to transmit sound by diaphragmatic action.

' 2. In combination with a wall having spaced furring strips on its face, a filling of low density sound absorbing material covering the wall face between the strips, a wire mesh stretched over said material and spaced from the wall by said strips, and an outer layer of acoustical plaster covering and keyed to said wire mesh, said outer layer being sufficiently flexible to be capable of transmitting sound by diaphragmatic action.

3. The combination of claim 2 in which said outer layer of acoustical plaster has perforations therethrough capable of passing sound.

4. In combination with a wall having spaced furring strips on its face and spaced projections on the outer face of said strips, a filling of low density sound absorbing material covering the wall face between said strips, a wire mesh secured to said projections and covering said sound absorbing material, and a layer of sound absorbing plaster covering and keyed to the wire mesh, said layer of plaster being relatively thicker over the furring strips than between said strips.

5. The combination of claim 4 in which the said. layer of sound absorbing plaster has perforations therethrough capable of passing sound.

CHARLES L. NEWPORT. HERBERT C. SMITH, 

